Gene
mutations are the reason black cats are black, according to new research.
The mutations appear to have arisen independently over time and are relatively
common in the cat species they affect. Interestingly, they are not all
alike. For instance, the gene that makes jaguars black is different from
the one that gives domestic kittens black fur.

Black fur clearly looks like something evolution has preserved, says
Stephen O'Brien, an expert in cat genetics at the US National Cancer Institute's
Laboratory of Genomic Diversity, in Frederick, Maryland, and a co-author
of the study.

For nocturnal big cats like jaguars and panthers, black fur might help
them blend in better with their surroundings, making them less visible
to prey and potential predators. But O'Brien says he doesn't believe camouflage
can fully account for the prevalence of dark fur in cats, especially big
ones.

The average jaguar doesn't fear much, says O’Brien, whose study
appears in Current Biology. “It's a killing machine that
has evolved to do just that.”

O’Brien offers another possibility: the mutations that make cats
dark also provide them with a survival advantage, such as protection from
infections.

O'Brien and his colleagues looked for genes that cause dark pelts, or
melanism, in three cat species: domestic felines, the jaguar and a South
American wildcat called the jaguarundi.

In jaguars and jaguarundis, dark pigment is linked to two different mutations
in the same gene, MC1R. MC1R belongs to a family of genes
that code for proteins called (seven-helix) transmembrane receptors that
stud the surface of cells. In humans, certain viruses, including HIV,
use these receptors to break into cells and hijack their DNA. People with
two mutant copies of the (seven-helix) transmembrane receptor CCR5 are
much less likely to become infected with HIV than those with normal versions
of the receptor.

Presumably, O'Brien says, some microbes that attack cats may find mutant
receptors in those animals less inviting, too. To test that theory, researchers
are considering a study of whether black cats are immune to feline HIV.

MC1R is also a pigment gene in humans. People with red hair and
pale skin have mutations that reduce the effect of the gene. The researchers
believe black fur in big cats reflects overactive MC1R.

The mutation that causes black fur in domestic cats involves a different
gene, called ASIP. Since five other cat species also have dark
coats, but not as a result of the three known gene mutations, at least
one other pigment mutation must affect felines.

The latest research is part of a larger effort at NCI to learn more
about human disease by studying cat genes.

Eduardo Eizirik, an NCI researcher who led the study, says scientists
have so far found about 260 inherited gene mutations that affect cats.
Scientists have looked at ten of those in depth, and all have counterparts
in humans.

Greg Barsh, a geneticist at Stanford University School of Medicine, who
studies pigment in mice, calls the latest study "fascinating."

Investigations of skin color genes in mice have led to insights about
the origins of obesity, neurodegenerative diseases, and basic cell biology,
Barsh says. "It's really interesting when one finds examples of genetic
changes in pigmentation in a natural population," he adds.